27 C.F.R. § 70.253
(b) Period when claim is filed. The 9-month period described in 26 U.S.C. 6532(c)(1) and paragraph (a) of this section shall be extended to the shorter of
(2) 6 months from the date of mailing by registered or certified mail by the appropriate TTB officer to the party claimant of a notice of disallowance of the part of the request to which the action relates. A request which, under § 70.167(b)(3) of this part, is not considered adequate does not extend the 9-month period described in paragraph (a) of this section.
(26 U.S.C. 6532)
Limitations on Credit or Refund
[T.D. ATF-301, 55 FR 47648, Nov. 14, 1990, as amended by T.D. ATF-450, 66 FR 29028, May 29, 2001]